Circuits may often be designed and tested using simulators prior to fabricating the circuits. The simulators may include a library of devices and parameters associated with the devices that can be used to design the circuit. The simulators can ensure that the circuit performs as expected and may emulate different phenomenon that can affect the circuit's performance. The simulators may analyze the operation of the circuit at discrete time steps (time-domain simulators).
Noise is a phenomenon that may affect the operation of a circuit. The noise power generated by a particular device may be independent of the frequency of the device (thermal noise) or may be dependent on the frequency (flicker noise). Noise may be simulated in the frequency domain. Emulating noise based on frequency limits analysis to small signal device operations (AC) and is not valid for any non-linear circuit behavior. Noise may also be simulated for circuits with periodic behavior, for example analyzing an oscillator at different points in a period.
Emulating noise in time domain is desirable. It is desirable to have general purpose noise emulation capabilities to simulate noise in linear and non-linear circuits that could be either periodic or non-periodic.